Portable communication devices, such as cellular telephones, use one or more power amplifiers to amplify an information signal prior to transmission. In some applications, an external voltage source is supplied to the power amplifier to provide the power amplifier with a reference voltage separate from a power supply voltage for the power amplifier. However, there are many applications in which a power amplifier may be implemented in a system that does not provide an external reference voltage. In such systems, the reference voltage must be generated on the power amplifier die, or chip.
Unfortunately, generating an accurate and stable reference voltage on the power amplifier chip can be problematic due to process, voltage and temperature (PVT) variations and other factors. This is particularly problematic in group III-V semiconductor manufacturing processes such as Gallium Arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) technology, which currently dominates the handset power amplifier market.
In addition, because the power supply voltage (typically provided by a battery) provided to a power amplifier circuit fluctuates in output voltage with use due to charge and drain cycles, providing a reference voltage that is independent of the fluctuation of the battery voltage is also problematic.
Therefore, it would be desirable to have a way of generating a stable reference voltage on a power amplifier chip.